Endogenous pacemakers and exogenous zeitgebers

Question 1

What does SCN stand for?

Answer 1

Suprachiasmatic Nucleus

Question 2

What is the SCN?

Answer 2

A tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain

Question 3

What is the SCN a type of?

Answer 3

One of the primary endogenous pacemakers in the mammalian species and is influential in maintaining security such as the sleep wake cycle

Question 4

Where is the SCN?

Answer 4

Nerve fibres connected to the eye cross in an area called the optic chiasm on their way to the visual area of the cerebral cortex and the SCN lies just above the optic chasm and receives information about light from this structure

Question 5

What happens with the SCN when are eyes are closed?

Answer 5

It continues enabling the biological clock to adjust to changing patters of day light

Question 6

What was DeCoursey’s research into the SCN?

Answer 6

He destroyed the SCN connection in the brains of 30 chipmunks who were returned to their natural habitat for 80 days

Question 7

What were DeCoursey’s results?

Answer 7

The sleep/wake cycle for the chipmunks disappeared and by the end of the study a significant proportion had been killed by predators

Question 8

What was Ralph et al’s research into the SCN?

Answer 8

He bred mutant hamsters with a 20 hour sleep/wake cycle
When SCN cells from foetal tissue were transplanted into the brain of normal hamsters the cycle of the normal group defaulted to 20 hours

Question 9

Where does the SCN pass its information on the length of day and light that it receives to?

Answer 9

The pineal gland

Question 10

What does the pineal gland do in the night?

Answer 10

Increases production of melatonin (a chemical that induces sleep and is inhibited during periods of weeks or less

Question 11

What has melatonin also been suggested as?

Answer 11

A casual factor in seasonal affective disorder

Question 12

What does the word Zeitgeber mean?

Answer 12

Time giver

Question 13

What are exogenous zeitgebers?

Answer 13

External factors in the environment that reset our body clock through a process known as entrainment

Question 14

What happens to the biological clock in the absence of external queues?

Answer 14

It continues to take in a distinct cyclical pattern and therefore sleeping and wakefulness would seem to be determined by the interaction between internal and external forces

Question 15

What is the role of light?

Answer 15

It is a key zeitgeber and can set the body’s main pacemaker so the SCN therefore plays a key role in the maintenance of the sleep/wake cycle

Question 16

What did Campbell and Murphy suggest about light?

Answer 16

That it may be detected by skin receptor sites in the body even when the same information is not sought by the eyes. 15 participants woke up when a bright light was shone on the back of their knees - a deviation in the usual sleep wake cycle happened, sometimes up th 3 hours
Suggesting light is a powerful zeitgeber

Question 17

What is an example of social cues affecting the cycle?

Answer 17

Babies started to develop circadian rhythms at 6 weeks and by 16 weeks most babies are entrained - this is likely to be influenced by the schedules imposed by parents
When travelling to other time zones by keeping to meal and bed times you can beat jet lag